Nuisance wood borers and seed insects in homes

John F. Kyhl and Jeffrey Hahn

There are several types of insects that may be brought into homes in wood (especially firewood and lumber), seeds, and nuts. These insects are a nuisance, and do not reinfest wood or other products. These insects should not be confused with powderpost or deathwatch beetles that can reinfest wood and cause extensive damage.

Identification of nuisance insects

One of the most common groups of nuisance wood borers is longhorned beetles (family Cerambycidae). These are medium to large (some are as large as 2 inches), dull to brightly colored insects. Longhorned beetles are recognized by their elongate oval body shape and long antennae (half the length of the body or longer). Commonly reported longhorned beetles in homes are the tanbark borer (Phymatodes testaceus) and the redheaded ash borer (Neoclytus acuminatus).

Metallic wood borers (family Buprestidae) get their name from the metallic sheen that many have as adults. These insects are medium to large (1½ inches), bullet to oval-shaped, with short antennae. The flatheaded appletree borer (Chrysobothris femorata) is a typical metallic wood borer that is occasionally found in structures in Minnesota.

Wood wasps (family Xiphydriidae) and horntails (family Siricidae) are both non-stinging wasps that bore into wood. Wood wasps are slender insects less than ¾ inch long that normally infect small branches of deciduous trees. Horntails are more than an inch long, and are recognized by a horn-like projection extending back from the abdomen. Horntails attack both deciduous and coniferous trees.

Bark beetles (family Scolytidae) are small (1/8-¼ inch long), robust reddish brown to black insects. They are very common in the landscape, and can emerge from many types of wood brought into homes.

Small to large parasitic wasps (families Braconidae and Ichneumonidae) that attack wood borers can also be found coming out of wood. They are small to large in size and can be differentiated from wood wasps by their constricted waists.

Weevils (family Curculionidae) are called snout beetles and are easily recognizable by the beak-like projection on their head. They are small (1/16-3/8 inch), dark beetles that feed in wood, seeds, and nuts. Small, whitish, legless weevil larvae may also be found in seed and nuts brought into homes.

Biology of nuisance insects

During the summer, most wood-boring insects feed in the wood and bark of trees and shrubs. These insects frequently spend the winter inside the tree as larvae or pupae, and emerge in the spring as adults. Many of these insects complete their life cycle in one year. However, when they are brought into homes in lumber or other wood products, they can finish development and can emerge at any time of year.

Most wood-boring insects prefer to attack trees or branches that are weak, drought-stricken, diseased, dying, or recently dead, and will also colonize trees that have recently been blown down or felled. Therefore, firewood or lumber taken from such trees is more likely to be infested than wood from healthy trees.

How nuisance insects get indoors

Insects are commonly brought in with firewood, but they can also be brought into homes in lumber used for construction or remodeling, decorative items (e.g. wreathes), and furniture. When trees are harvested and milled into lumber, insects that were feeding in the tree at the time of harvest remain inside after the tree is processed. Some insects continue to develop and complete their life cycle once the lumber is used in the house. These insects can cause concern to homeowners (but little economic damage) as they bore out of the wood and anything that covers it (e.g., drywall, linoleum, paneling, or moldings). These insects will not reinfest wood in structures after they emerge.

Insects can also enter homes inside acorns, nuts, or seeds brought in for decoration or as food. Most of these insects are weevils, and are found as legless, plump, white grubs. They crawl out of acorns or nuts and attempt to hide under rugs or other objects. These grubs develop into long-snouted adult weevils. Other nuts or seeds such as hazelnuts, walnuts, or honeylocust pods can contain similar insects.

Damage

Wood-boring insects tunnel in the wood as they feed. In most cases, the damage is cosmetic and does not affect the structure of the wood. The only damage noticed is generally the exit holes formed when the adults emerge from the wood.

Emerging insects do not re-infest wood in homes. Adults have very specific requirements for oviposition; they lay their eggs only in the bark of green wood. These insects do not lay eggs on logs without bark, dried, sawed, painted, or finished wood. Generally, only a few insects emerge, although there are exceptions when larger numbers are seen.

Control

No insecticide treatments are needed to control these nuisance wood borers and seed insects. They will eventually die or go away on their own without being anything more than a temporary nuisance. When nuisance wood borers and seed insects appear, just physically remove them by hand or with a vacuum. Remember that these insects are harmless to humans and cannot infest seasoned wood.

The best way to manage these pests is to prevent them from coming into homes. To prevent insects from coming in with firewood, leave the wood outside or in an unheated shed or garage. Bring in a small supply as it is needed. This way the wood will be burned before the insects emerge. To prevent them from being imported when remodeling or replacing infested wood, use only kiln-dried lumber. Do not treat logs or lumber with insecticides to control these insects.